docs: def scale_atoms(fac):
      '''Scale the currently selected atoms atoms by a certain factor
      *fac*.
  
      Use the value *fac=1.0* to reset the scale.
  
      '''
      rep = current_representation()
      atms = selected_atoms()
      rep.scale_factors[atms] = fac
      
      rep.update_scale_factors(rep.scale_factors)
      viewer.update()